Seal ring holder for membrane element and membrane element

ABSTRACT

A seal ring holder for membrane elements which is capable of attaining an increase in the area of membranes packed per element; and a membrane element using the seal ring holder, are provided. The seal ring holder for membrane elements which is disposed at an end part of a spiral wound membrane element to hold a ring seal ring on the outer periphery thereof while allowing a raw liquid to flow into a membrane end part of the membrane element, includes: a first ring part which has a side wall facing an upstream-side membrane end part of the membrane element and is inserted into an end part of a sheathing member of the membrane element; a projecting ring part which has been formed upstream from the first ring part and has side walls respectively on both sides, an edge face of the sheathing member and the downstream-side edge face of the seal ring being fixable respectively to the side walls; a second ring part which is formed upstream from the projecting ring part and to the outer periphery of which the seal ring is to be fitted; and a third ring part which is formed upstream from the second ring part and to which the upstream-side end face of the seal ring is fixable.

FIELD OF THE INVENTION

The present invention relates to a seal ring holder which holds a sealring for closing the space between a spiral wound membrane element and avessel, and a membrane element using the seal ring holder. Moreparticularly, the present invention relates to a seal ring holder withwhich a membrane element can have a larger amount of a membrane part(membrane leaves) packed therein than before, and a membrane element.

DESCRIPTION OF THE RELATED ART

Spiral wound separation membrane modules have hitherto been used in awide range of applications such as the desalting of brine or seawater,production of ultrapure water, and wastewater treatments. As shown inFIG. 9, spiral wound separation membrane modules have a structure whichcomprises a pressure vessel 1 and a spiral wound separation membraneelement E housed therein and in which the space between the vessel 1 andthe element E has been closed with a ring seal ring 4 so that a rawliquid 7 supplied is caused to efficiently flow into the element E. Theraw liquid which has flowed into the element E is separated with theseparation membrane while flowing downstream along the feed-side passagematerial of the element E. The permeated liquid which has passed throughthe separation membrane flows along the permeation-side passage materialand collected in a water-collecting tube. The membrane part of theelement E is constituted of a wound structure 2 including wound membraneleaves each comprising a feed-side passage material, a separationmembrane, and a permeation-side passage material which have beensuperposed.

FIG. 9 shows the state of an end part of the module in which the elementE has been fitted into the vessel 1 and a raw liquid 7 is supplied. Theend part has such a constitution that the raw liquid 7 supplied isinhibited by the seal ring 4 from passing outside the element E and iscaused to wholly flow into the element. The element E has a seal ringholder 10 so that the seal ring 4 is held on the element E.

The seal ring 4 is held by the seal ring holder 10 attached to an endpart of the element E. The seal ring 4 is made of, e.g., a rubber andhas a U- or V-shaped section. Upon reception of the pressure of a waterflow, the seal ring 4 expands outward and in this state, seals the spacebetween itself and the vessel 1.

The seal ring holder 10 generally has a cylindrical part 19 (skirt) forfitting thereinto an end part of the wound structure 2 constituting themembrane part. Namely, the seal ring holder 10 has such a structure thatthe sheathing member 5 of the element E can be fitted and bonded to theouter periphery of this cylindrical part 19. However, the structure inwhich the wound structure 2 is inserted into the cylindrical part 19 hashad a drawback that the diameter of the wound structure 2 is limitedand, hence, to increase the membrane area is limited. In addition, theaxis-direction dimension of the wound structure 2 is limited by thethickness of the seal ring holder 10. Although it is hence desirablethat the seal ring holder 10 have a smaller thickness, the seal ringholder 10 needs to have at least a certain thickness because it shouldhave a groove formed therein for holding the seal ring 4 and have thestrength required of seal ring holders.

On the other hand, treatments with separation membranes are required toattain reduction in the cost of the treatment system. One of thesubjects therefor is to increase the area of membranes packed perelement. For attaining this, it is necessary to increase the volume ofmembrane leaves which can be packed. There is hence a desire for adiminution in limitations by the members used.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide a sealring holder for membrane elements, which is capable of attaining anincrease in the area of membranes packed per element.

Another object of the present invention is to provide a membrane elementusing the seal ring holder.

Those objects can be accomplished with the present invention, which isas follows.

The present invention provides a seal ring holder for membrane elementswhich is disposed at an end part of a spiral wound membrane element tohold a ring seal ring on the outer periphery thereof while allowing araw liquid to flow into a membrane end part of the membrane element, theseal ring holder comprising:

a first ring part which has a side wall facing an upstream-side membraneend part of the membrane element and is to be inserted into an end partof a sheathing member of the membrane element;

a projecting ring part which has been formed upstream from the firstring part and has side walls respectively on both sides, an edge face ofthe sheathing member and the downstream-side edge face of the seal ringbeing fixable respectively to the side walls;

a second ring part which has been formed upstream from the projectingring part and to the outer periphery of which the seal ring is to befitted; and

a third ring part which has been formed upstream from the second ringpart and to which the upstream-side end face of the seal ring isfixable.

In the seal ring holder of the present invention, the first ring parthas a side wall facing an upstream-side membrane end part of themembrane element and does not have a structure in which the membrane endpart is inserted into the ring part. Because of this, the membrane part(wound structure) can have a larger diameter. Furthermore, the firstring part can be inserted into and fixed to the sheathing member, and aseal ring can be fitted to and held on the outer periphery of the secondring part. Because of this, the width (thickness) of the remainingparts, i.e., the projecting ring part and the third ring part, can bereduced and the axis-direction length of the membrane part can beincreased accordingly. As a result, the area of membranes packed perelement can be increased.

In the constitution described above, the outer diameter of the thirdring part preferably is smaller than the outer diameter of theprojecting ring part. When the seal ring holder has this structure, thespace between the third ring part and the vessel is increased. Becauseof this, when a seal ring having a U- or V-shaped section is used, it ismore apt to receive the flow or pressure of a raw liquid and, in anoutward spread state, performs its sealing function with highercertainty.

Furthermore, it is preferred that the width of the projecting ring partbe smaller than the width of the second ring part and the width of thethird ring part be smaller than the width of the second ring part, eachwidth being the width as measured in a direction parallel to the axis ofthe membrane element. When the seal ring holder has this structure, theparts other than the seal ring-holding groove can have a reduced widthwhile securing the seal ring-holding groove, whereby the axis-directionlength of the membrane part can be increased and the area of membranespacked can be increased.

It is preferred that a plurality of peripheral groove parts on whichheight of a peripheral surface was partially low, or cut parts in whichthe ring part was partially discontinued are disposed at the third ringpart. This constitution enables the space between the third ring partand the vessel to partially spread. As a result, when using a seal ringhaving U- or V-shaped cross-section, it becomes easy to receive the flowor pressure of a raw liquid, and in an outward spread state, it canexhibit its sealing function further certainly.

Furthermore, it is preferred that a plurality of edge groove partsextending from inner circumference to outer circumference are disposedat the edge of the third ring part. In the case of connecting aplurality of membrane elements, the edges are closely contacted witheach other in the conventional constitution. As a result, there is theproblem that it is difficult to discharge liquid when discharging theliquid in the membrane element when, for example, washing. However, itis possible to smoothly discharge the inner liquid by disposing aplurality of the edge groove parts (this is the same even when the ringpart has the discontinued cut parts). In the case that rapid pressurechange is applied, high pressure difference generates between the insideand the outside of the sheathing member of the membrane element, andthis may lead to the danger of breakage of the membrane element.However, since the liquid passes through the disposed edge groove partsto smoothly flow to the outside of the element, there is no possibilityof danger.

The present invention further provides a membrane element whichcomprises a spiral wound membrane element and the seal ring holder formembrane elements which is disposed upstream from an upstream-sidemembrane end part of the element, wherein the first ring part isinserted into an end part of the sheathing member of the element.

Since the membrane element of the present invention uses the seal ringholder of the present invention, it can attain an increase in the areaof membranes packed therein, as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a half of an example of the seal ringholder for membrane elements of the present invention which is in anattached state.

FIG. 2 is views showing an example of the seal ring holder for membraneelements of the present invention: 2A is a left-side view; 2B is asectional view of the seal ring holder taken in the direction of thearrows I—I; and 2C is a right-side view.

FIG. 3 is a sectional view illustrating a half of another example of theseal ring holder for membrane elements of the present invention.

FIGS. 4A and 4B are views showing important parts of other examples ofthe seal ring holder for membrane elements of the present invention.

FIGS. 5A, 5B, 5C, 5D and 5E are views important parts of other examplesof the seal ring holder for membrane elements of the present invention.

FIG. 6 is views showing other example of the seal ring holder formembrane elements of the present invention: 6A is a left-side view; 6Bis a sectional view of the seal ring holder taken in the direction ofthe arrows I—I; and 6C is a sectional view of the seal ring holder takenin the direction of the arrows II—II.

FIG. 7 is views showing other example of the seal ring holder formembrane elements of the present invention: 7A is a view correspondingto the sectional view of the seal ring holder taken in the direction ofthe arrows I—I in FIGS. 6; and 7B is a view corresponding to thesectional view of the seal ring holder taken in the direction of thearrows II—II 9 in FIG. 6.

FIG. 8 is a sectional view illustrating a half of an example ofconventional seal ring holders for membrane elements.

FIG. 9 is a sectional view showing part of a conventional seal ringholder for membrane elements which is in an attached state.

In the drawings:

2 membrane part of membrane element (wound structure)

4 seal ring

5 sheathing member

10 seal ring holder

11 first ring part

11 a side wall of first ring part

12 projecting ring part

13 second ring part

14 third ring part

14 c peripheral groove part on third ring part

14 d cut portion on third ring part

14 e edge groove part on third ring part

E membrane element

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be explained below byreference to the accompanying drawings. FIG. 1 is a sectional viewshowing a half of an example of the seal ring holder for membraneelements of the present invention which is in an attached state. FIG. 2is views showing an example of the seal ring holder for membraneelements of the present invention: 2A is a left-side view; 2B is asectional view of the seal ring holder taken in the direction of thearrows I—I; and 2C is a right-side view.

As shown in FIG. 1, the seal ring holder of the present invention isdisposed at an end part of a spiral wound membrane element E and servesto hold a ring seal ring on the outer periphery thereof while allowing araw liquid to flow into a membrane end part of the membrane element E.On the other hand, the membrane element of the present inventioncomprises a spiral wound membrane element E and the seal ring holder 10of the present invention disposed upstream from an upstream-sidemembrane end part of the element E, wherein the first ring part 11 hasbeen inserted into an end part of the sheathing member 5.

The membrane element E may be any element which is a so-called spiralwound membrane element. For example, the membrane part is constituted ofa wound structure 2 comprising a central tube (water-collecting tube 6)and, wound therearound, membrane leaves each comprising a feed-sidepassage material, a separation membrane, and a permeation-side passagematerial which have been superposed. Each membrane leaf has a sealedstructure which prevents a raw liquid from directly flowing from thefeed-side passage into the permeation-side passage. Because of thisconstitution, the raw liquid which has flowed into the membrane elementE is separated with the separation membranes while flowing downstreamalong the feed-side passage materials of the element E. The permeatedliquid which has passed through the separation membranes flows along thepermeation-side passage materials and collected in the water-collectingtube.

A seal ring 4 is held by the seal ring holder 10 attached to an end partof the membrane element E. The seal ring 4 may have a circular,elliptic, square, or similar section. In the present invention, however,a seal ring 4 having a shape with an open part, such as one having a U-or V-shaped or similar section, is preferred. The seal ring 4 preferablyis made of an elastic material such as a rubber, elastomer, or resin.The seal ring 4 having a U- or V-shaped or similar section expandsoutward upon reception of the pressure of a water flow and can, in thisstate, seal ring the space between itself and the vessel.

The sheathing member 5 that can be used is, for example, a structureformed by directly winding a tape or sheet of a fiber-reinforced resinon the membrane element E. It is preferred that an end part of thesheathing member 5 be fixed by bonding or the like to the first ringpart 11 of the seal ring holder 10.

The water-collecting tube 6 has holes arranged at appropriate intervals,and is made of, e.g., a resin. Before the water-collecting tube 6 isused, the upstream-side end thereof is sealed with, e.g., a plug inorder to prevent the raw liquid from flowing thereinto.

As shown in FIG. 2, the seal ring holder of the present inventioncomprises: a first ring part 11 which has a side wall 11 a facing anupstream-side membrane end part of a membrane element E and is insertedinto an end part of a sheathing member 5 of the membrane element E; aprojecting ring part 12 which is formed upstream from the first ringpart 11 and has side walls respectively on both sides, an edge face ofthe sheathing member 5 and the downstream-side edge face of a seal ring4 being fixable respectively to the side walls; a second ring part 13which is formed upstream from the projecting ring part 12 and to theouter periphery of which the seal ring 4 is fitted; and a third ringpart 14 which is formed upstream from the second ring part 13 and towhich the upstream-side end face of the seal ring is fixable. The sealring holder of the present invention thus has a structure having noskirt part into which the wound structure 2 including membrane leaves isfitted.

With respect to dimensions (widths as measured in a direction parallelto the axis of the membrane element E) of the parts described above, thewidth of the projecting ring part 12 is preferably smaller than thewidth of the second ring part 13. Furthermore, the width of the thirdring part 14 is preferably smaller than the width of the second ringpart 13.

Specifically, the widths of the first ring part 11, projecting ring part12, second ring part 13, and third ring part 14 are preferably 5–8 mm,3–5 mm, 7–8 mm, and 3–5 mm, respectively. When these parts have suchdimensions, the seal ring holder as a whole can have a width (thickness)as small as 15–30 mm while securing both the groove into which a sealring 4 is fitted and a bonding allowance for the sheathing member 5.

It is preferred in the present invention that the outer diameter of thethird ring part 14 be smaller than the outer diameter of the projectingring part 12. In this constitution, the upstream-side wall of the groovefor holding a seal ring 4 is lower and, hence, the seal ring 4 is moreapt to receive a water flow.

This embodiment has a perforated plate 15 having openings 15 a as astructure which allows a raw liquid to flow into a membrane end part ofthe membrane element E. When the perforated plate 15 is used, the flowrate distribution of the raw liquid flowing into the membrane part ofthe membrane element E can be easily controlled by changing the size,positions, density, etc., of the openings 15 a. It should, however, benoted that the structure for raw-liquid introduction in the presentinvention should not be construed as being limited to the perforatedplate 15, and any appropriate structure such as radially arranged spokesmay be used in place of the perforated plate 15.

Preferably, the perforated plate 15 has a cylindrical part 16 at thecenter thereof and the seal ring holder is disposed, with thewater-collecting tube 6 being inserted into this cylindrical part 16.The cylindrical part 16 and the water-collecting tube 6 may be fixed toeach other by bonding, etc.

In the embodiment shown in FIG. 1, the water-collecting tube 6 isdisposed so that the upstream-side end thereof is flush with theupstream-side end of the side wall of the third ring part 14 of the sealring holder 10, and the upstream-side end of the cylindrical part 16 islocated downstream from these. Similarly, at the downstream-side of theelement, the downstream-side end of the water-collecting tube isdisposed so as to be flush with the downstream-side end of the side wallof the downstream-side seal carrier. However, by disposing thewater-collecting tube 6 so that the upstream-side end thereof is locateddownstream from the side wall of the third ring part 14 (i.e., locatedcloser to the perforated plate), the length of the wound structure 2 asthe membrane part can be made larger for the water-collecting tube 6.

The perforated plate 15 has radially arranged ribs 17 on its membraneelement side. These ribs 17 reinforce the perforated plate 15, wherebythe total width of the two members can be reduced.

The seal ring holder 10 can be formed from a thermoplastic resin,thermosetting resin, heat-resistant resin, or the like by a conventionaltechnique such as injection molding.

Other embodiments of the present invention will be explained below.

(1) The embodiment described above is one in which the seal ring holderfor membrane elements has the minimum thickness. However, a seal ringholder having the structure shown in FIG. 3, which is formed bymodifying the conventional seal ring holder by eliminating the skirt andforming a first ring part 11, may be used. Use of this seal ring holdereliminates the necessity of fitting a wound structure 2 includingmembrane leaves into the skirt and makes it possible to use amembrane-leaf wound structure 2 having a larger diameter than onesheretofore in use.

(2) It is preferred in the present invention that the width of thesecond ring part 13, which corresponds to the width of the groove forholding the seal ring 4, be made close to the thickness of the seal ring4 as shown in FIGS. 4A and 4B, so as to reduce the overall thickness ofthe seal ring holder. In this case, it is preferred that the height ofthe third ring part 14, which is located upstream, be reduced in orderto prevent the third ring part 14 from blocking a water flow to the sealring 14 and that the third ring part 14 be made to have a taper surfacein order to enable the seal ring 4 to be more apt to receive a waterflow. Examples of the taper surface include a taper surface 14 a havinga section with a curved contour and a taper surface 14 b having asection with a linear contour.

(3) Furthermore, it is preferred that the first ring part 11, whichcorresponds to a bonding allowance for the sheathing member 5, besubjected to groove formation, notching, surface roughening, or the likefor the purpose of enhancing bonding strength, as shown in FIGS. 4A and4B.

As shown in FIGS. 5A–5E, it is preferred that a portion P1 which fixesthe seal ring holder 10 and the wound structure 2 and a portion P2 whichfixes the seal ring holder 10 and the sheathing member 5 are disposed onthe first ring part 11. The bonding allowance between the seal ringholder 10 and the sheathing member 5 of the first ring part 11 has arole to strongly adhere the seal ring holder 10 and the sheathing member5 and maintain its adhered state. In coating the sheathing member 5, apressure-sensitive adhesive tape, a glass cloth or the like is wound atthe faced portion of the sheathing member 5 and the wound structure 2 tofix those. This fixing is also necessary to prevent influx of the resinfrom the faced portion to the edge of the wound structure.

Further, as shown in FIGS. 5A–5E, it is preferred that the portionfixing the seal ring holder 10 has a step mark such that apressure-sensitive adhesive tape or the like does not drop off, or has ataper becoming deeply toward the direction of the projecting ring part.In addition, it is preferred that the part adhering the sheathing memberand maintaining the same has a structure such that a step mark isprovided on the adhered portion so as not to cause deviation in ashearing direction, thereby maintaining the same against a partingforce.

(4) As shown in FIGS. 6A–6C, a plurality of peripheral groove parts 14 con which height of a peripheral surface was partially low may bedisposed on the third ring part 14. Further, as shown in FIGS. 7A–7C,cut parts 14 d in which the ring part was partially discontinued may bedisposed on the third ring part 14. The depth of the peripheral groovepart 14 c is preferably 0.5–3 mm. The number of the peripheral grooveparts 14 c disposed is preferably 4 or more, and more preferably 6–16.

(5) On the other hand, as shown in FIGS. 6A–6C, a plurality of edgegroove parts 14 c extending from inner circumference to outercircumference may be disposed at the edge of the third ring part 14. Thecut parts 14 d in the third ring part 14 shown in FIG. 7B also have thefunction as the edge groove part extending from inner circumference toouter circumference. To facilitate inflow and outflow of water insideand outside the membrane element, the edge groove parts 14 e arearranged radially with a uniform distance in the number of preferably 4or more, and more preferably 6–16.

In the connecting portion of the membrane element, where width W1 on anedge between a groove and the adjacent groove is 1, the width W of theedge grove part 14 e is preferably 0.9 or less to the width W1 such thatrecesses and projections of the edge groove parts 14 e do not overlap.

The present invention is described in more detail by reference to thefollowing Examples, but it should be understood that the invention isnot construed as being limited thereto.

EXAMPLE 1

A seal ring holder having the structure shown in FIG. 2 was produced.This seal ring holder had no skirt and had the following dimensions.Overall thickness (same as the thickness from the surface for butt jointwith wound-structure end face): 20 mm, bonding allowance for sheathingmember: 6 mm, width of seal ring groove: 8 mm, depth of seal ringgroove: 6.5 mm, upstream-side wall height of seal ring groove: 3.5 mm.

COMPARATIVE EXAMPLE 1

A conventional seal ring holder having the structure shown in FIG. 8 wasproduced. This seal ring holder had a skirt having an inner diameter of194 mm, and had the following dimensions. Overall thickness: 48 mm,thickness from the surface for butt joint with wound-structure end face:37 mm, bonding allowance for sheathing member (including the skirtpart): 27 mm, width of seal ring groove: 9 mm, depth of seal ringgroove: 6.5 mm. The upstream-side wall was equal in height to thedownstream-side wall.

ELEMENT PRODUCTION EXAMPLE

The seal ring holders obtained in Example 1 and Comparative Example 1were used to produce spiral wound membrane elements. Membraneleaf-constituting members having the same thickness were used inproducing each spiral wound membrane element. A membrane having a lengthof 1,480 mm was folded double, with a raw-water passage material beingsandwiched therebetween, to produce a unit leaf. Such unit leaves werewound around a water-collecting tube together with a permeatedwater-passage material. Results of a comparison between the two systemsare shown in the Table below.

The wound structure including 33 leaves had a diameter of 197 mm.Although this wound structure could not be fitted with the conventionalseal ring holder of Comparative Example 1, the seal ring holder ofExample 1 according to the present invention could be attached thereto.The element produced with the conventional seal ring holder contained 31leaves. Namely, the number of membrane leaves could be increased by 2.The membrane leaf width heretofore in use could be increased by 37 mm,resulting in an increase in total membrane area of 4.6 m². Furthermore,the area of the membranes effective in actual treatment, i.e., the areaobtained by subtracting the loss due to the membrane leaf bonding parts,increased by 4.2 m².

TABLE Comparative Example 1 Example 1 Number of membrane leaves 33 31Diameter of wound structure (mm) 197 189 Width of membrane leaf (mm) 975938 Area of membranes used (m²) 47.6 43.0 Effective area of membranes(m²) 41.7 37.5

It should further be apparent to those skilled in the art that variouschanges in form and detail of the invention as shown and described abovemay be made. It is intended that such changes be included within thespirit and scope of the claims appended hereto.

1. A seal ring holder for membrane elements which is disposed at an endpart of a spiral wound membrane element to hold a seal ring on the outerperiphery thereof while allowing a raw liquid to flow into a membraneend part of the membrane element, the seal ring holder comprising: afirst ring part which has a side wall facing an upstream-side membraneend part of the membrane element and is inserted into an end part of asheathing member of the membrane element; a projecting ring part whichis formed upstream from the first ring part and has side wallsrespectively on both sides, an edge face of the sheathing member and thedownstream-side edge face of the seal ring being fixable respectively tothe side walls; a second ring part which is formed upstream from theprojecting ring part and to the outer periphery of the second ring partthe seal ring is fitted; and a third ring part which has been formedupstream from the second ring part and to the third ring part theupstream-side end face of the seal ring is fixable, wherein a pluralityof peripheral groove parts on which height of a peripheral surface waspartially low or cut parts in which the ring shape of the cut parts arepartially discontinued are disposed on the third ring part.
 2. The sealring holder for membrane elements as claimed in claim 1, wherein theouter diameter of the third ring part is smaller than the outer diameterof the projecting ring part.
 3. The seal ring holder for membraneelements as claimed in claim 2, wherein the width of the projecting ringpart is smaller than the width of the second ring part and the width ofthe third ring part is smaller than the width of the second ring part,each width being the width as measured in a direction parallel to theaxis of the membrane element.
 4. The seal ring holder for membraneelements as claimed in claim 1, wherein the width of the projecting ringpart is smaller than the width of the second ring part and the width ofthe third ring part is smaller than the width of the second ring part,each width being the width as measured in a direction parallel to theaxis of the membrane element.
 5. The seal ring holder for membraneelements as claimed in claim 1, wherein a plurality of edge groove partsextending from inner circumference to outer circumference are disposedat the edge of the third ring part.
 6. A membrane element comprising aspiral wound membrane element and the seal ring holder for membraneelements as claimed in claim 1 disposed upstream from an upstream-sidemembrane end part of the spiral wound membrane element, wherein thefirst ring part has been inserted into an end part of a sheathing memberof the spiral wound membrane element.
 7. A seal ring holder for membraneelements which is disposed at an end part of a spiral wound membraneelement to hold a seal ring on the outer periphery thereof whileallowing a raw liquid to flow into a membrane end part of the membraneelement, the seal ring holder comprising: a first ring part which has aside wall facing an upstream-side membrane end part of the membraneelement and is inserted into an end part of a sheathing member of themembrane element; a projecting ring part which is formed upstream fromthe first ring part and has side walls respectively on both sides, anedge face of the sheathing member and the downstream-side edge face ofthe seal ring being fixable respectively to the side walls; a secondring part which is formed upstream from the projecting ring part and tothe outer periphery of the second ring part the seal ring is fitted; anda third ring part which has been formed upstream from the second ringpart and to the third ring part the upstream-side end face of the sealring is fixable, wherein a plurality of edge groove parts extending frominner circumference to outer circumference are disposed at the edge ofthe third ring part.
 8. The seal ring holder for membrane elements asclaimed in claim 7, wherein the outer diameter of the third ring part issmaller than the outer diameter of the projecting ring part.
 9. The sealring holder for membrane elements as claimed in claim 8, wherein thewidth of the projecting ring part is smaller than the width of thesecond ring part and the width of the third ring part is smaller thanthe width of the second ring part, each width being the width asmeasured in a direction parallel to the axis of the membrane element.10. The seal ring holder for membrane elements as claimed in claim 7,wherein the width of the projecting ring part is smaller than the widthof the second ring part and the width of the third ring part is smallerthan the width of the second ring part, each width being the width asmeasured in a direction parallel to the axis of the membrane element.11. A membrane element comprising a spiral wound membrane element andthe seal ring holder for membrane elements as claimed in claim 7disposed upstream from an upstream-side membrane end part of the spiralwound membrane element, wherein the first ring part has been insertedinto an end part of a sheathing member of the spiral wound membraneelement.